How we solved this problem on recent project...
I think I can help! We just did this on a DV short that we needed to put on VHS. We shot 16:9 using a DVC-Pro camera. Not sure if this is the best way, but it worked for us!
You're camera has the kind of 16:9 mode that works by stretching the picture to fill a 4:3 frame (which is why it looks stretched in the viewfinder). If you attempt to play this tape back on any monitor that doesn't have 16:9 capability, it will look "stretched". This is because you have actually recorded a 4:3 picture, but the camera electronically stretches and squishes it to take advantage of the most pixels available. You've got more pixels this way, which means more "data", and better quality. This is better than simple "letterboxing" or "masking" the frame which is what many consumer cameras do. The important thing to remember is that no matter what happens, you actually are editing a 4:3 piece of data.
Now what happens when you edit? Your edit system (in this case Premiere) lets you "tell" it that you're using a 16:9 video so it "displays" the picture "squished" while you're editing, so it looks "correct" on screen. Whatever you put in, Premiere will display in a 16:9 window, regardless of what the aspect was when you shot. Since you did shoot in 16:9, it looks correct when Premiere does this. The key thing to remember is, you still have a 4:3 picture, Premiere is just showing it to in 16:9 format.
SO, if you plan to lay this off to any kind of deck that doesn't natively record/display in 16:9 format (such as VHS) you are going to need to use an effects program to change the vertical size of the image. You can do this right in Premiere, we used BorisFX because we were editing in Media100. Basically, you have to process the entire movie so the picture is 100% Horizontal size and 74.2% Vertical (not sure about that number) size. Then you can spit it out to whatever 4:3 tape format you want and it will be letterboxed. However, it will now be letterboxed not matter what you play it on, even 16:9 monitor.
If you want to make a digital file, QuickTime, WMV, whatever, it shoudl be simpler. Just export the movie with it's height as 74.2% of its width. Or if you have high-quality uncompressed file already, you should be able to run it through something like Cleaner to do the size conversion.
Hope this helps!